The synthesis and processing of nuclear ribosomal RNA (rRNA) and heterogeneous RNA (hnRNA) will be studied in vivo in partially hepatectomized rats and in vitro in L1210 tumor cells. (3H)-Orotic acid and (3-H)-uridine will be used to pulse label and measure the synthesis of various species of nuclear RNA in rat liver and L1210, respectively. The methylation of rRNA and hnRNa, as well as the polyadenylation of hnRNA will be examined as representative post-transcriptional processes. The nucleoside antibiotic, cordycepin (3'-deoxyadenosine), will be used to examine its specific inhibitory action on rRNA and poly(A)-and poly(A) plus hnRNA in the presence and absence of the adenosine deaminase inhibitor 2'-deoxycoformycin.